1. Technical Field of the Invention
This invention relates to working vehicles such as agricultural vehicles and light civil engineering vehicles. More particularly, the invention relates to a working vehicle of the frameless type that uses a case block of a hydrostatic stepless transmission hereinafter abbreviated as HST) as a body forming member for connecting a front vehicle body and a rear vehicle body.
2. Description of the Related Art
A working vehicle of the frameless type (e.g. a frameless type tractor) as noted above may have a reduced number of components and a reduced number of steps for assembling the components to long frames extending between the front vehicle body and rear vehicle body, compared with a frame type tractor carrying an engine and an HST. Thus, the frameless type working vehicle is attracting attention as a working vehicle having advantages distinct from the tractor of the type having body frames.
A conventional frameless type tractor has a body structure as disclosed in Japanese patent laying-open publication H11-91380 (or U.S. Pat. No. 6,250,414 which has a priority claim from the Japanese application), for example. This known vehicle body structure includes a front body having an engine, and a rear body having a transmission case. Connected in series between the front body and rear body are a clutch housing containing a main clutch for connecting and disconnecting engine drive, and a case block acting as an HST.
In the above conventional structure, however, the case block acting as an HST is connected to the front and rear vehicle bodies through a relatively large number of connecting positions and relatively small connecting areas. Consequently, the conventional structure has a drawback in strength, and a drawback in manufacture, i.e. difficulty to attain assembling accuracy.
The object of this invention is to secure a necessary strength and precision in assembly, and to facilitate an operation to connect a front vehicle body and a rear vehicle body by effectively utilizing an HST case block acting as an intermediate vehicle body interconnecting the front and rear vehicle bodies.
The above object is fulfilled, according to this invention, by a working vehicle comprising:
an engine;
a main clutch for connecting and disconnecting drive from the engine;
a hydrostatic stepless transmission with a pump and a motor for changing speed of the drive transmitted from the main clutch;
a front vehicle body supporting the engine;
a rear vehicle body comprising a transmission case housing a propelling transmission for receiving speed-changed drive from the hydrostatic stepless transmission; and
an intermediate vehicle body connected to the front vehicle body and the rear vehicle body to constitute a body of the working vehicle in combination with the front vehicle body and the rear vehicle body;
wherein the intermediate vehicle body comprises a case block housing the hydrostatic stepless transmission;
the case block includes, formed integral with one another, a small diameter portion connected to the rear vehicle body and providing case walls for the pump and the motor, a large diameter portion connected to the front vehicle body and having an upper edge at a higher level than an upper surface of the small diameter portion, and a transitional portion disposed between the small diameter portion and the large diameter portion; and
the large diameter portion defines an accommodating space for the main clutch.
With the above construction, the case block of the HST includes the large diameter portion formed integral with the small diameter portion and transitional portion, and having an upper edge higher than the upper surface of a change speed block portion providing case walls for the pump and motor. Consequently, the case block has an enlarged area for connection to the front vehicle body, to realize an improved connecting strength.
Since the case block has, as an integral part thereof, the large diameter portion having an accommodating space of the main clutch, one connecting position is omitted from the construction in that there is no need for connection to a clutch housing. In this sense also, connecting strength may be improved.
The vehicle body structure according to this invention is advantageous in that the above aspects produce a multiplier effect to improve connecting strength and reduce the number of connecting steps.
Where the case block is connected to the front vehicle body, the main clutch is linked not through a rotary shaft acting as an input to the pump of the HST, but through a transmission shaft interlocked to a transmission gear on the rotary shaft. That is, the main clutch fixed to the front vehicle body different from the case block is connected, through a gear transmission mechanism, using the main clutch transmission shaft which provides some flexibility for accuracy, rather than the input shaft of the pump which requires assembling accuracy. Thus, where the case block is connected to the front vehicle body, a connection is not made that would require a very high degree of accuracy such as fitting the pump input shaft adjacent a bearing fixed to the case. Instead, drive transmission is made through a connection between the transmission shaft and a component of the main clutch, which allows a relatively good assembling adaptability.
Thus, the vehicle body structure according to this invention is advantageous in reducing the required assembling accuracy to some extent, and realizing a simplified assembling process.
The transitional portion may have an upper surface in form of an inclined wall so that the case block has a sectional profile gradually changing from the small diameter portion to the large diameter portion. This construction provides an advantage of forming a smooth transition from the small diameter portion to the large diameter portion without impairing the case strength.
On the other hand, the small diameter portion, the large diameter portion and the transitional portion may have respective lower surfaces at an equal level. This assures simplicity of an assembling process, and necessary strength. Moreover, a sufficient ground height may readily be secured for the vehicle to run smoothly despite ruggedness of the ground.
In the working vehicle according to this invention, a shaft supporting wall portion is provided in a case interior including the inclined wall, for supporting a main clutch transmission shaft for outputting engine drive from the main clutch, and a pump rotary shaft provided for the pump as an input shaft of the hydrostatic stepless transmission for receiving the engine drive.
Generally, the inclined wall where the sectional profile of the case gradually changes from the small diameter portion to the large diameter portion tends to have reduced strength. However, according to this invention, the shaft supporting wall portion formed in the case interior reinforces the case interior including the inclined wall. Not only is the above inconvenience in strength avoided, but also the strength of the case block itself may be improved by the shaft supporting wall portion.
In the working vehicle according to this invention, the shaft supporting wall portion includes:
a first partition having bearings for supporting forward ends of the pump rotary shaft and a motor rotary shaft provided for the motor as an output shaft of the hydrostatic stepless transmission;
a second partition having a bearing for supporting a rearward end of a transmission gear mounted on an end of the pump rotary shaft extending through the first partition, and a bearing for supporting a rearward end of a transmission gear formed on a rear end region of the main clutch transmission shaft; and
a third partition having bearings for supporting forward regions of the transmission gears, and dividing an arranging space of the transmission gears from the accommodating space of the main clutch;
the third partition having a lid member detachably attached to the second partition.
By employing the above construction, the shaft supporting wall portion may be formed of a combination of the first, second and third partitions, instead of a single partition. This reinforces an increased area where the sectional profile of the case block changes, to minimize low strength parts. By reinforcing an increased area where the sectional profile of the case block changes, the strength of the case block may be further increased.
A different feature of this invention resides in that the arranging space of the transmission gears communicates, for allowing a circulation of pressure oil, with a change speed chamber space formed in the small diameter portion for housing the pump and the motor of the main propelling change speed device.
By employing the above construction, pressure oil is allowed to circulate between the gear arranging space defined by the shaft supporting wall portion of the case block and the change speed chamber space housing the pump and the motor of the HST. This dispenses with oil piping from the HST to the gear arranging space, and oil piping from the gear arranging space to the change speed chamber space. Thus, lubricating oil passages may be provided without requiring a complicated piping structure. Further, a space capacity is enlarged by substantially integrating the gear arranging space to the change speed chamber space. This easily avoids such an inconvenience as a sharp increase in the temperature of lubricating oil which could occur in a small gear arranging space not communicating with the change speed chamber space.
A further feature of this invention resides in that the pump rotary shaft has an axis located below and offset to one side transversely of the vehicle body from an axis of the main clutch transmission shaft, and the motor rotary shaft has an axis located below and offset to the other side transversely of the vehicle body from the axis of the pump rotary shaft.
By employing the above construction, compared with a construction where the axis of the pump rotary shaft is located directly under the axis of the main clutch transmission shaft, the two axes may be vertically spaced from each other by a reduced distance, slightly reduced as it may be. In addition, the axis of the pump rotary shaft may be offset transversely of the vehicle body from the axis of the main clutch transmission shaft. As a result, the entire case block may have a reduced vertical dimension. Moreover, with the axis of the pump rotary shaft offset to one side transversely of the vehicle body, the axis of the motor rotary shaft may be offset a small amount to the other side from the axis of the main clutch transmission shaft. This is advantageous in reducing the transverse dimension of the case block as a whole.
Further, in the relation between the axis of the pump rotary shaft and the axis of the motor rotary shaft, the latter is placed below the former. Compared with the case where the two shafts are juxtaposed horizontally, the case block may have a reduced transverse dimension.
Other features, functions, effects and advantages of the present invention will be appreciated upon reading the following description with reference to the accompanying drawings.